The present invention, in some embodiments thereof, relates to a particle focusing and, more particularly, but not exclusively, to methods and systems of acoustic focusing.
Aerodynamic focusing is a mechanism that has been widely used to produce particle beams, for example tightly collimated particle beams. Using the aerodynamic lenses, near-axis particles can be focused onto a streamline in principle. An aerodynamic lens system typically consists of three parts: a flow control orifice, focusing lenses, and an acceleration nozzle. The choked inlet orifice fixes the mass flow rate through the system and reduces pressure from ambient to the value required to achieve aerodynamic focusing. The focusing lenses are a series of orifices contained in a tube that create converging-diverging flow accelerations and decelerations, through which particles are separated from the carrier gas due to their inertia and focused into a tight particle beam. The accelerating nozzle controls the operating pressure within the lens assembly and accelerates particles to downstream destinations. Aerodynamic lenses have been widely used in particle mass spectrometers. Available designs for aerodynamic lenses effectively collimate particles as small as 30 nm.
At present, focusing of a range of micron and submicron size aerosol particles is carried out using aerodynamic forces in periodic aerodynamic lens arrays, see Liu, P., Ziemann, P. J., Kittelson, D. B. and McMurry, P. H. (1995) Aerosol Sci. Techn., 22, 293-3 13 and Wang, X., Gidwani, A., Girshick, S. L. and McMurry, P. H. (2005). Aerosol Sci. Techn., 39, 624-636., which are incorporated herein by reference. Such arrays are used as inlets to on-line single-particle analyzers; see Wexler, A. S. and Johnston, M. V. (2001) in Aerosol Measurement: Principles, Techniques, and Applications. P. A. Baron and K. Willeke ed., Wiley, New York, which is incorporated herein by reference.
Hydrodynamic focusing is a technique usually used to provide results from flow cytometers or Coulter counters for determining the size of bacteria or cells. When using Hydrodynamic focusing for flow cytometry microscopic particles, such as cells and chromosomes, are counted and examined by suspending them in a stream of fluid and passing them by an electronic detection apparatus.
Acoustic focusing, such as Acoustic cytometry, is a technology that is used for focusing cells or particles with acoustic radiation pressure forces. For example acoustic focusing is employed in flow cytometry analysis, either as a substitute for hydrodynamic focusing or in combination with it, is described in Curr. Protoc. Cytom. 49:1.22.1-1.22.12. © 2009 by John Wiley & Sons, Inc, which is incorporated herein by reference. The use of acoustic standing waves to concentrate initially homogeneously suspended aerosol or hydrosol particles in acoustic pressure nodal or antinodal planes was first visualized by Kundt (1866) and then described by and Rayleigh (1945). Subsequent works utilize this phenomenon (see Duhin, 1960; Czyz, H., 1990; Dain et al., 1995; Vainshtein et al., 1996 and papers cited therein) for various applications. The acoustic force was also used to position and levitate particles (see King, 1934; Fuchs, 1964; Coakley et al., 1989; Gopinath and Mills, 1994; Hertz, 1995 and papers cited therein). In those works the particle motion was studied in situations when undisturbed fluid was at rest. A number of devices and method have been used to use acoustic waves to concentrate aerosol or hydrosol particles. An example of using acoustic focusing technology is described in U.S Patent Application Publication number 2010/0009333, filed on 17 Jun. 2009 that describes methods for using acoustic focusing technology on its own or in conjunction with hydrodynamic focusing for analyzing biological samples. In one application, a preferential orientation of biological particles is achieved by applying a substantially elliptical acoustic field. The application describes a sample comprising a fluid medium carrying a plurality of discrete biological particles which are pre-concentrated in-line with a sample analyzer, such as a flow cytometer, where a sheath fluid is introduced after acoustic pre-concentration. The application describes methods for acoustically separating suspended discrete biological particles of different densities from a fluid medium.